ANALYST: This has become a 'trust us' story

The CFO of auction house Sotheby's, Patrick McClymont, has resigned from the company effective January 1, and that's giving some on Wall Street pause.

"...yes we were surprised by the resignation," analysts at Stifel wrote after the news broke.

Sotheby's "has, to some extent, become more of a “trust us” story given the added leverage, use of guarantees, and expansion of SFS," they wrote.

SFS is the auction house's financing business, and its fast growth has raised concerns that the company could take on too much debt. SFS has "some additional risks if the art cycle rolls hard in 2016," Stifel wrote.

"We saw Mr. McClymont as an important part of the transition to modernize the business practices. Also, the CFO slot being in transition will limit the chance for more meaningful strategic updates around real estate, the loan portfolio, or any sale to a trophy buyer."

McClymont's departure, plus any departures that will come after Sotheby's offered employees buyouts in November, could mean the auction house loses business next year.

Sotheby's CEO Tad Smith admitted that his customers have become more "discerning" in this market, and Stifel says that it "continues to hear more skepticism from big collectors around current auction / dealer pricing in the art market."